The present invention relates to a buildup board. The present invention also relates to an electronic component having a buildup board, such as a package module, e.g., a ball grid array (“BGA”) package, and a printed board mounted with the package module, and an electronic apparatus, such as a personal computer (“PC”), a server, a cellular phone, and a digital camera.
A BGA package has conventionally been used to meet a demand for a small and high-performance electronic apparatus. In general, the BGA package is one type of a package module that is mounted with an IC or LSI that serves as a CPU on a package board, and soldered to a printed board (also referred to as a “system board” or “motherboard”). The BGA package can realize the high performance and miniaturization of the electronic apparatus through the high density of the package.
The recent BGA packages often use a buildup board. The buildup board includes a double-sided printed board or multilayer printed board as a core, and adheres a buildup layer to one surface or both surfaces of the core. The buildup layer is an alternate pile of insulating layers and wiring layers, and has a via hole as a plated throughhole for an interfacial connection. The double-sided adhesions can balance the warp. The next generation BGA package is expected to have a higher transmission characteristic. Prior art suggest various methods for improving the transmission characteristic by thinning the core layer, by reducing a specific via hole diameter, or by modifying a physical property value.
The prior art include, for example, Japanese Utility-Model Applications, Publication Nos. 5-63076 and 6-13181, and Japanese Patent Applications, Publication Nos. 7-202359, 7-221510, and 2005-236064.
However, thinning of the core layer has a limit of the strength. In addition, a shape balance among plural via holes also influences the transmission characteristic, and thus a reduction of the specific via hole diameter is also subject to the restriction. Moreover, a change of the physical property value associates with changes of base materials of the core layer and the buildup layer to a low melting point material and a low loss material, but it is difficult to develop a base material that dramatically changes the conventional low melting point material and low loss material. From these restrictions, the prior art methods cannot significantly improve the transmission characteristic. In addition, the prior art methods significantly change the manufacturing method of the multilayer substrate, and problematically increase the cost.